Dental implants serve as foundations for a variety of dental prostheses, including crowns and bridges. Although implants may be made in a variety of forms, a conventional implant has a generally cylindrical body that is externally threaded, and is surgically fixed into the patient's healthy bone tissue. The implant also includes a top portion comprising a cavity having an internal thread, and a structure adapted to receive an insertion tool. The insertion tool engages the top portion and facilitates insertion of the implant into the bone. Insertion often includes rotating the implant so that the external threads pull the implant into the bone. The insertion tool is removed from the implant after insertion. The implant may even include an external coating, such as hydroxyapatite or a titanium plasma spray, which enables bone tissue to integrate better with the implant, thereby providing enhanced support for the prosthesis.
A surgeon prepares the implant site by first incising the gingival tissue at the implant site and then drilling a substantially cylindrical bore into the bone mass. The surgeon positions the implant over the bore and screws the externally threaded implant into the bone tissue. The surgeon typically uses a ratcheting or rotating tool to screw the implant into the bone. The ratcheting tool may directly engage the implant but, for convenience, the ratcheting tool often imparts torque to a driver that is removably secured to the top portion of the implant. The driver transmits the torque to the implant. The driver includes a bottom portion that is configured to matingly engage the top end of the implant. The implant and driver may be secured together by a retaining screw to form an assembly. The assembly facilitates delivery of the implant to the surgical site. After fixing the implant into the bone, the driver is removed from the implant and the surgical site is closed and allowed to heal after which the gingival tissue over the implant is incised to expose the implant. At this time, a permanent abutment is secured to the top end of the implant. Importantly, the abutment must not move relative to the implant. To this end, a fixation screw engages internal threads of the implant and fixes the abutment to the implant. The bottom portion of the abutment may include a Morse taper that cold welds the abutment to the implant as the fixation screw is tightened.
Examples of driver-less systems include U.S. Pat. No. 4,960,381 to Niznick and U.S. Pat. No. 6,464,500 to Popovic. Niznick teaches a dental implant having an externally threaded surface and an internal structure for engaging an insertion tool. The top end of the implant is open and in registry with an internally-threaded portion. The top end also includes a hex-shaped cavity in its inner wall surfaces for receiving a hex wrench. The internal hex-shaped configuration is intended to allow the insertion of the implant in the jawbone of a patient using an Allen-type wrench. Stress concentrations along the hex corners have resulted in numerous implant fractures.
Popovic describes a dental implant having an externally threaded surface and an internal structure for engaging an insertion tool. The top end of the implant includes an internally threaded portion. A hex-shaped cavity is located below the internally threaded portion for the purpose of receiving a hex wrench. The hex-shaped cavity is below the internally threaded portion, so the distance between corners of the hex-shaped cavity is smaller than the internally threaded portion. The hex-shaped cavity is therefore so small that at normal insertion torques, damage may occur to the insertion tool or the insert. As a result, the direct connection of the insert with the insertion tool is problematic.
Surgeons generally prefer systems that include drivers over systems that are driver-less. Drivers reduce stress concentrations while setting the implant and facilitate implantation by permitting the insertion tool to remain above the gum line. Driver-containing systems typically include an implant defining an internal cavity with a top end having a chamfered surface. The driver is removably fixed to the implant, such as with a retaining screw. The chamfered surface is of sufficient size and depth to afford lateral stability to any driver inserted into the cavity. The driver obviously increases the cost of the implant system.
The implant, driver, abutment, retaining screw, and fixation screw usually comprise titanium and are individually costly to produce. To reduce cost and complexity, manufacturers have attempted to use the driver as an abutment and the retaining screw as the fixation screw. Unfortunately, the driver must be removable from the implant but the abutment should be permanently fixed and immobile. Previous attempts to produce a single driver/abutment device have proven inadequate. While being used as a driver, the device can cold weld to the implant thereby negatively affecting removability. While being used as an abutment, the device can retain mobility thereby jeopardizing the prosthetic. A need exists for a driver/abutment device that is easily removable when setting the implant but fixedly secured when used as a permanent abutment.